When a color is keyed out and replaced with video footage, it is known as which type of key?

When a color is keyed out and replaced with video footage, it is known as which type of key?

• A. Luma key
• B. Chroma key
• C. Alpha key
• D. Depth key

Answer: (B)

Chroma keying is the technique of removing a specific color from the foreground so that replacement video can show behind it. This is exactly what happens when someone is filmed in front of a green or blue screen and that color is digitally erased to reveal a different background. The key is based on hue values—the color you choose to remove—with adjustments for tolerance and spill to clean up edges. Luma key, by contrast, uses brightness information to mask parts of the image, not color. An alpha key relies on an existing transparency channel (the matte) rather than a color being removed. A depth key uses depth information to separate elements by distance from the camera, which is a more specialized effect.

Chroma keying is the technique of removing a specific color from the foreground so that replacement video can show behind it. This is exactly what happens when someone is filmed in front of a green or blue screen and that color is digitally erased to reveal a different background. The key is based on hue values—the color you choose to remove—with adjustments for tolerance and spill to clean up edges.

Luma key, by contrast, uses brightness information to mask parts of the image, not color. An alpha key relies on an existing transparency channel (the matte) rather than a color being removed. A depth key uses depth information to separate elements by distance from the camera, which is a more specialized effect.